A commonly available design for a refrigeration appliance, particularly one for consumer use, includes a cabinet that contains a freezer compartment and a fresh food compartment. These compartments may be arranged e.g., side by side or may include one over the other. In one example of a conventional design, the evaporator portion of a refrigeration loop is positioned in the freezer compartment where a fan moves air in the freezer compartment across the evaporator to freeze the contents of the freezer compartment. A damper positioned between the freezer compartment and the fresh food compartment is used to feed a portion of the air over to the fresh food compartment for cooling its contents. Typically, the damper is moved between a fully open or fully closed position.
To control the refrigeration loop that provides cooling for the refrigerator, one previous approach has been the use of a single thermostat such as e.g., a bimetallic thermostat. The compressor is cycled on or off based on the temperature of the thermostat. Among several drawbacks to this approach is that the measurement of temperature is limited to a single location within the appliance, which can lead to undesirable temperature gradients within the compartments. Another drawback is that repeated cycling of the compressor and/or evaporator fan between on and off states typically results in large temperature swings and intermittencies in air flow, which in turn also causes poor humidity control.
A more modern approach to control includes the use of refrigerators having microcontrollers that execute a wide variety of various algorithms for temperature control of the appliance. For many of these algorithms, the available actuators for the control system are used as either binary state devices (on/off) or sometimes as quaternary state devices (off/low/medium/high). For example, a fan for the evaporator would either be in an “on” or “off” state. A damper would be either fully shut or fully closed. As such, the effectiveness of these control systems and their respective algorithms is limited by operating in such finite states rather than in continuous actuation.
Therefore, a control system for a refrigerator appliance would be useful. More particularly, a control system for a refrigerator that can use temperature measurements from e.g., both the freezer and fresh food compartments would be useful. Such a control system that can provide for continuous adjustment of multiple actuators (e.g., the compressor, damper, and evaporator fan) to more accurately regulate the temperature in the fresh food and freezer compartments would be beneficial. Such a control system that can operate the refrigerator appliance in a more energy efficient manner would also be useful.